Flip chip interconnections made to connect a semiconductor die pad circuit to a semiconductor supporting substrate have historically been made with exotic plating methods and reflow solder attachment. More recently electrically conductive epoxy has been used to make the flip chip interconnections. These conductive epoxy interconnects have typically been plagued with high contact resistance. For example, when used to contact an aluminum bond pad, which is the semiconductor industry standard, a tenacious nonconductive oxide coated surface forms in a short amount of time, even at room temperature. Because of the nonconductive oxides present, electrically conductive epoxies on otherwise bare aluminum form an interconnect having an extremely high contact resistance. The resistance typically ranges from hundreds of ohms to millions of ohms.
In an effort to reduce the contact resistance a more noble metal, such as gold, has been used to provide a very inert, oxide free surface over which the conductive epoxy may be applied. Gold precludes the formation of nonconductive metal oxides at the surface of the contact. Thus gold, plated on an existing contact, has a direct low contact resistance when it is bonded with a conductive epoxy. However the gold plating of a semiconductor die pad is an elaborate process that can be very difficult, expensive and time consuming. It is very difficult because the process is typically not an electroless deposition process and therefore requires the substrates to be electrically connected to a power supply.
In another method to reduce the contact resistance the oxide formed during the epoxy application is mechanically removed, typically with abrasive action. In a further method the base metal is subjected to a chemical pre-treatment to prohibit oxide formation.
Therefore there exists a need for a flip-chip surface mount device wherein a supporting substrate and a die pad are epoxy bonded efficiently with a low contact resistance.